Fair Value Measurement - Nonrecurring Basis (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities without readily determinable fair values		$ 2,368,000,000	$ 2,441,000,000
Net losses as a result of measurement alternative		(301,000,000)	(42,000,000)
Net gains as a result of measurement alternative		$ 167,000,000	243,000,000
Residential mortgage | Broker price opinion | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, liquidation value discount		13.00%
Residential mortgage | Broker price opinion | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, liquidation value discount		46.00%
Residential mortgage | Broker price opinion | Weighted average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, liquidation value discount		27.00%
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		$ 3,567,000,000	4,788,000,000
Total liabilities measured at fair value on a nonrecurring basis		12,000,000	0
Total nonrecurring fair value gains/(losses)		(933,000,000)	(92,000,000)	$ 64,000,000
Nonrecurring | Accounts payable and other liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities measured at fair value on a nonrecurring basis		12,000,000
Total nonrecurring fair value gains/(losses)		(11,000,000)	0	0
Nonrecurring | Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		2,583,000,000	3,731,000,000
Total nonrecurring fair value gains/(losses)		(393,000,000)	(274,000,000)	(68,000,000)
Nonrecurring | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		984,000,000	1,057,000,000
Total nonrecurring fair value gains/(losses)		(529,000,000)	182,000,000	132,000,000
Net losses as a result of measurement alternative		(134,000,000)
Net gains as a result of measurement alternative	$ 505,000,000		201,000,000	$ 149,000,000
Nonrecurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		0	0
Total liabilities measured at fair value on a nonrecurring basis		0
Nonrecurring | Level 1 | Accounts payable and other liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities measured at fair value on a nonrecurring basis		0
Nonrecurring | Level 1 | Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		0	0
Nonrecurring | Level 1 | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		0	0
Nonrecurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		1,616,000,000	3,476,000,000
Total liabilities measured at fair value on a nonrecurring basis		0
Nonrecurring | Level 2 | Accounts payable and other liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities measured at fair value on a nonrecurring basis		0
Nonrecurring | Level 2 | Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		1,611,000,000	3,462,000,000
Nonrecurring | Level 2 | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		5,000,000	14,000,000
Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		1,951,000,000	1,312,000,000
Total liabilities measured at fair value on a nonrecurring basis		12,000,000
Nonrecurring | Level 3 | Accounts payable and other liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities measured at fair value on a nonrecurring basis		12,000,000
Nonrecurring | Level 3 | Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		972,000,000	269,000,000
Nonrecurring | Level 3 | Residential mortgage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		602,000,000
Nonrecurring | Level 3 | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a nonrecurring basis		979,000,000	$ 1,043,000,000
Equity securities without readily determinable fair values		$ 535,000,000